The structure and primary reactions of the monoxygenase heme proteins are worthy of multiple approach and access. They participate in the ubiquitously critical processes of dioxygen reduction, stereo selective synthesis in the mammal effector molecules, and the cycling of carbon residues. We propose for the next year or two to focus our inquiry along three primary lines. 1. An immediate target is the primary structure of the 45,000 dalton heme sulfur protein, P450cam. A parallel aim is to reveal the loci of cysteine sulfhydryl residues, their role in regulation substrate affinity, and electron flow, and behavior as the fifth (axial) ligand of the heme iron. 2. Additional stable isotope replacements are required to enhance resonance Raman, NMR, and EPR measurement for active site structure elucidation. Now in process are S34/32, Fe 54/57, N 15/14, and H 2/1. 3. Emphasis will be placed on probing the "active oxygen" structure and mechanism of action on hydrocarbon functional groups subsequent to the second transfer of reducing an equivalent from the Fe2S2Cys4 center. Low temperature cosolvent stabilized oxy complexes (half life greater than or equal to hours at minus 20C) will be supplement by single oxygen chemical donors to ferric heme. Explorations on four electron oxygen reducing systems will be extended and first papers submitted.